The smartphone war is heating up, and although it is still unclear where Windows Phone, BlackBerry, and Web OS will eventually fit into the crowded mobile operating system market, it is very clear that iOS and Android are the market share leaders.

Gartner reports that Google and Apple are the “obvious winners” in the smartphone category. The combined share of iOS and Android doubled to nearly 62 percent in Q2 2011, up from just over 31 percent in the same quarter last year. Google’s mobile operating system now accounts for 43.4 percent of all smartphone sales, up from 17.2 percent in Q2 2010; and Apple reached 18.2 percent, up from 14.1 percent at the same time.

Many app developers ask me for my perspective on how to develop and scale a profitable user acquisition strategy for their app. One of the primary gaps in knowledge I see from app developers is a clear understanding of how the operating system impacts user acquisition.

As the first post in a two-part series, we’ll explore how the iOS operating system impacts user acquisition for apps. For the second post, we’ll focus on how the Android operating system impacts user acquisition for apps.

How Differences in Smartphone Operating Systems Impact App Promotion

Smartphones as a whole skew to a younger audience – 18 to 34.

Source: Pew Internet & American Life Project, as reported by eMarketer

IOS devices have a hands-down great user experience, but at a higher price. With elegant style and the best integrated hardware and software, iOS devices are the simplest to operate. Apple oversees a more regulated, closed environment than Google. This creates positives and negatives. For example, users can only buy apps through the App Store, making the transaction more streamlined and thus driving significantly higher conversion rates for premium billing or in-app purchasing because Apple has so many credit cards on file. Apple also regulates the apps that are listed in the App Store based upon its App Store Review Guidelines, making it problematic for some new apps to get published, as they must play by Apple’s rules. To complicate things even more, Apple’s rules are not always black and white and are subject to Apple’s evolving interpretation.

Key Points About User Acquisition on iOS

Because of the reliance on a centralized App Store for all user acquisition, it is important to rank high overall or in your category for driving organic traffic.

Popularity also impacts where you rank in search results, another driver of organic traffic.

Editorial features in iTunes can drive significant installs. “The only promotion we’ve found to be consistently effective in driving paid downloads has been promotion via iTunes, either as a ‘Staff Favorite’ or a ‘New & Noteworthy’ selection on iTunes itself. The reasons and process by which Apple makes these selections are a mystery to us, but we have found it useful to always consider Apple’s interests when positioning a new product,” said Paul O’Connor, brand director, Appy Entertainment, developer of Trucks and Skulls, FaceFighter, and Tune Runner, all featured in iTunes.

Third-party ad networks, especially those focused on apps, perform well to drive user acquisition. Seek performance-based campaigns, whether CPC or CPI, with these networks. Be mindful of limitations in behavioral ad targeting.

The social impact on user acquisition for apps (i.e., the viral coefficient) is not as strong in iOS as it is for Facebook, but one marketer at a leading social game recently told me that they get a 3/10 viral coefficient (i.e., for every 10 new users they acquired outside of social means, they get their audience to incite three more users to play with them). I would speculate that Zynga’s Words With Friends has a much higher coefficient than the average on iOS. Read more about “How Mobile is Getting More Social.”

iOS Demographics

Possibly because of the higher price of devices, iPhones skew to higher income users.

Source: The Nielsen Company

IPhone users buy more paid apps – half of them buy at least one per month – compared with 21 percent of Android users and 35 percent of iPod touch users.

IPhone users are the most loyal at 91 percent, iPod touch at 88 percent, and Android at 84 percent.

As far as mobile ads, the average click-through rate (CTR) is 0.52 percent. IPhone users are by far more willing to click on ads, with an average CTR of 0.78 percent, while Android users are at 0.47 percent.

IPod touch skews to a young audience – 65 percent are 17 and younger, according to a chart from AdMob.

IPod touch users love their apps – especially free apps, downloading an average of 12 apps a month – 37 percent more apps than iPhone and Android users. They also spend more time using them: 100 minutes a day.

For the second post , we’ll focus on how the Android operating system impacts user acquisition for apps.